An image forming apparatus such as a copy machine, a printer and a multifunction printer is classified into an ink-jet type, an electro-photographic type and a thermal transfer type according to an image forming method. In the electro-photographic image forming apparatus, an image is formed on a printing medium through a series of processes such as charging, exposing, developing, transferring and fixing.
A conventional electro-photographic image forming apparatus is configured with a cartridge assembly in which a drum unit and a developing unit are integrally formed, wherein the drum unit has a photosensitive drum, a charging roller, a transfer roller and so on, and the developing unit accommodates a developer therein and has a developing roller and a supply roller.
Here, the cartridge assembly has a developer comprised of toner and carrier for a printing operation. The developer should be replenished or replaced due to consumption of the toner resulting from printing operation.
Formerly, the replenishment or replacement of the developer was performed by collecting and discharging a waste developer, i.e., waste toner and waste carrier simultaneously and then replenishing a new developer. However, in such a developer replenishing or replacing method, a large amount of the developer is abandoned, and a separate waste developer receiving part is required.
In Japanese Patent Publication No. 1993-66659 (Patent document 1), there is disclosed an image forming apparatus in which the toner is collected and reused in consideration of a conventional developer consumption. Patent document 1 discloses a process cartridge in which a waste toner tank is integrally installed at a photosensitive drum, and a discharging system for collecting the waste toner in the waste toner tank into a developing machine is installed.
However, according to patent document 1, a toner consumption may be reduced by collecting and reusing the toner, but there is a problem in that the quality of an image is degraded over time by reduction of the carrier and deterioration of the developer which result from long-term use.
Meanwhile, in Japanese Patent Publication No. 2001-194908 (Patent document 2), there is disclosed an image forming apparatus in which the toner is collected and reused, and a supply amount of the carrier is controlled. Therefore, it is possible to solve the carrier reduction problem in Patent document 1.
However, in Patent document 2, since there is not a separate developer discharging structure other than a structure for scraping the developer remaining in the drum and collecting the developer, there is a problem in that the quality of an image is degraded by deterioration of the developer due to long-term use, and a separate toner and carrier receiving part is required.
Also, in the image forming apparatuses of the above-described patent documents, when it is necessary to disassemble or detach a drum unit, a developing unit, a developer collecting unit and a main body of the image forming apparatus which are independently or integrally formed, a shutter is installed at a moving route of the developer. Here, a unit for collecting the developer is assembled or detach in a lengthwise direction of a unit for discharging the developer or from a lower side thereof. At this time, the shutter is opened and closed, and thus some of the developer drops down. That is, in the conventional image forming apparatus, there is a problem in that the developer leaks when the units or the unit and the main body are detach from each other.